1. Field of the Invention
This invention relates to the chemical embossing of polyvinyl chloride (PVC) articles such as those in the form of a panel, sheet or film.
2. Background Art
The traditional method to impart surface texture to PVC articles is by embossing. Illustratively, typical printed and unprinted PVC articles, e.g., films used for lamination to metal, wood, plastics, wallboard, and the like, require an embossed surface to give the film a textured look.
Embossing is normally a mechanical method by which a thermoplastic sheet is textured with a pattern imparted by an embossing roll pressed against a backup roll under controlled preheating and post cooling conditions. When it is desired to provide color contrast to the embossed area, inks are used in order to accentuate the embossing.
A problem involved with such mechanical embossing is in placing the ink in registration with the embossed areas. Such registration is difficult to accomplish, requires expensive equipment and is generally limited to small embossed patterns.
One process for obtaining registration of ink with a mechanically embossed pattern is called "spanished". In the spanished process, the PVC substrate is embossed mechanically to form valleys or depressed areas. Then, the surface is flooded with ink. The ink is subsequently squeegeed off so that it is wiped off of the hills or raised portions of the substrate but remains in the valleys. A major shortcoming of the spanished process is streaking of ink on the substrate.
In addition to mechanical embossing as described above, an embossing effect can be obtained chemically on certain substrates. Generally, chemical embossing involves adding a surface tension reducer to an ink or over a specific pattern which is printed on a substrate. A top coat is then applied so that it superimposes at least a portion of the area having the reduced surface tension. The surface tension of the top coat is selected so that it does not wet the area which has the reduced surface tension but it does wet the substrate and other portions overlying the substrate which do not have the reduced surface tension. On drying, the top coat pulls away from the area which has the reduced surface tension and leaves a valley or depression which forms the embossed area in the coating.
Many attempts to produce a desirable chemically embossed surface on PVC substrate by applicant were unsuccessful. Tests showed that compatibility was a problem as between the PVC substrate, the type of ink, the type of surface tension reducing agent, and the top coat. Thus, the ink, with or without a surface tension reducing agent, may not be compatible with the substrate or the top coat. Some surface tension reducing agents are not compatible with certain inks and some top coats are not compatible with the PVC substrate. Also, the top coat would spread unevenly in the areas of the reduced surface tension. If the surface tension of the top coat were lowered, then the top coat did not coat evenly on the PVC substrate. Finally a combination of certain inks, surface agent reducing agents and top coat was found to be operable.
A search revealed the following references which deal with chemical embossing.
U.S. Pat. No. 4,532,157 to H. Schmidt et al. of Jul. 30, 1985 relates to a process for producing colored, resin-impregnated paper sheets with a three-dimensional surface structure by printing a pattern on the paper sheets wherein the printing ink includes a lacquer repelling material in those regions where the lacquer is to be thinner than in other regions, then drying the printed sheet and finally lacquering the printed sheet.
U.S. Pat. No. 4,735,827 to J Frank et al. of Apr. 5, 1988 relates to a process for preparing a graphic pattern on a carrier having a protective coating thereon in exact registration with the pattern. The Frank et al. process comprises: applying a liquid protective coating over a graphic pattern on a carrier slightly beyond the edge definition of the pattern and in substantial registration therewith, the protective coating having sufficient surface tension to wet the graphic pattern but not the surface of the carrier. When the protective coating is dried, it dewets and retracts from the surface of the carrier onto the graphic pattern and provides exact registration therewith.
The Frank et al. process differs from the present invention in a number of ways. Thus, the entire substrate is siliconized in the above Frank et al. patent whereas the silicone is placed in the ink forming the pattern or image of the present invention; the substrate in Frank et al. is polyester and not PVC; the protective coating in Frank et al. is placed in the area of the pattern instead of over the entire surface, and the protective coating in Frank et al. does not come in contact with the substrate material.
U.S. Pat. No. 5,019,202 to I. Kawahata et al. of May 28, 1991 relates to a process for producing decorative sheets having an embossed pattern corresponding to a printed pattern layer by forming a printed pattern layer of ink and resin on base paper wherein the printing ink is liquid repellant; coating the whole surface of the printed pattern layer with top coat and then solidifying the top coat thereby forming a top coat of which the portions corresponding to the liquid repellant printed pattern layer are concave. The resin is used with the ink in order to provide strength to the paper.
Japanese patent JP-297391 of Jul. 10, 1987 to Toyota Jidosha relates to the use of a surface tension conditioner such as silicone oil which is used to form a pattern on a base material. A metallic paint is then coated over a base material and the pattern. The metallic paint which is overcoated on the surface tension conditioned layer has a different orientation from that of the metallic paint which is coated directly on to the base material.
The silicone oils of this invention are used as anti-foam agents in compositions having the same ingredients as those of this invention. However, the silicone oil for defoaming purposes is used in such small quantity, e.g., a few tenths of a percent, so that it does not provide the function of preventing wetting as in the present invention.
U.S. Pat. No. 4,343,839 of Aug. 10, 1982 and its divisional U.S. Pat. Nos. 4,365,039 and 4,374,167 of Dec. 21, 1982 and Feb. 15, 1983 respectively, all to J. R. Blegen, describe vapor permeation curable polyester resin compositions for coating flexible substrates such as PVC. The coating composition is that of certain phenolic terminated polyesters and multi-isocyanate curing agents. U.S. Pat. No. 4,368,222 of Jan. 11, 1983 which issued to J. R. Blegen et al. describes similar coating compositions of a phenolic terminated polyester and multi-isocyanates. The coating compositions of these Blegen patents and the polyester containing coatings of the Blegan et al. patent are used as the top coat in this invention and are referred to herein simply as aromatic-hydroxyl functional polyester-isocyanate top coats.